IBC

Hi Brendan,
Magnetic north differs from true north by a declination that varies depending on the site location as well as fluctuations in the Earth’s magnetic field over long periods of time. True north is a constant and refers to the geographic North Pole. Magnetic north tends to shift and refers to the pole of the Earth's magnetic field. In mid 2002, true north and magnetic north were approximately 590 miles apart. Property line bearings in the Denver area are typically related to the bearings of section lines since most of the major roadways were originally deeded along those section lines. In theory, a section would be exactly 1 mile square, but do to factors like topography, the curvature of the Earth and sometimes really old private surveys, this varies. A township is also roughly square and consists of 36 sections. Townships are identified being relative to a baseline and a meridian (i.e. latitude/longitude). Correspondingly the bearings of the section lines are relative to the latitude/longitude of the Earth. However, the Earth is round, maps are flat, and the curvature of the Earth becomes noticeable once you get into larger land surveys. So, started in 1807 by Thomas Jefferson as the Survey of the Coast, the National Geodetic Survey was given the task of establishing a land survey/coordinate system for the Country and the survey expanded westerly as the Country grew. A geodetic survey is a survey of a large area of land in which corrections (i.e. the sections are more trapezoidal than square) are made to account for the curvature of the Earth.

In response to your question, I would have to say technically neither. The rotation is based on a bearing of N 0d E being Geodetic North. For whatever application Ryan is working on though, I would say that geodetic north more closely resembles true north rather than magnetic north. I hope that was enough detail. Let me know if you have any other questions.
Thanks, phil

RedSox wrote:I sent an email to the civil engineer asking whether the North we were using was magnetic north or true north (because the contractor asked). Here is the answer I received.

Hi Brendan,
Magnetic north differs from true north by a declination that varies depending on the site location as well as fluctuations in the Earth’s magnetic field over long periods of time. True north is a constant and refers to the geographic North Pole. Magnetic north tends to shift and refers to the pole of the Earth's magnetic field. In mid 2002, true north and magnetic north were approximately 590 miles apart. Property line bearings in the Denver area are typically related to the bearings of section lines since most of the major roadways were originally deeded along those section lines. In theory, a section would be exactly 1 mile square, but do to factors like topography, the curvature of the Earth and sometimes really old private surveys, this varies. A township is also roughly square and consists of 36 sections. Townships are identified being relative to a baseline and a meridian (i.e. latitude/longitude). Correspondingly the bearings of the section lines are relative to the latitude/longitude of the Earth. However, the Earth is round, maps are flat, and the curvature of the Earth becomes noticeable once you get into larger land surveys. So, started in 1807 by Thomas Jefferson as the Survey of the Coast, the National Geodetic Survey was given the task of establishing a land survey/coordinate system for the Country and the survey expanded westerly as the Country grew. A geodetic survey is a survey of a large area of land in which corrections (i.e. the sections are more trapezoidal than square) are made to account for the curvature of the Earth.

In response to your question, I would have to say technically neither. The rotation is based on a bearing of N 0d E being Geodetic North. For whatever application Ryan is working on though, I would say that geodetic north more closely resembles true north rather than magnetic north. I hope that was enough detail. Let me know if you have any other questions.
Thanks, phil